Characterization study of candidate technologies for nuclear material quantification in fuel debris at Fukushima Daiichi Nuclear Power Station, 2; Passive neutron technique (Interim report)

Nomi, Takayoshi ; Nagatani, Taketeru ; Shiromo, Hideo ; Asano, Takashi 

This report describes applicability evaluation results of the passive neutron technique (PN) for characterization study of candidate technologies for nuclear material quantification in fuel debris at Fukushima Daiichi Nuclear Power Station. The PN consists of Differential Die-away Self-Interrogation (DDSI) and neutron coincidence counting. The DDSI evaluates the neutron multiplication and absorption effect and corrected coincidence count rate determines Cm-244 effective mass. Nuclear material is quantified by using isotopic composition from code calculation or ray measurement. The simulation results indicate that the PN is applicable to B-10 contained fuel debris. The results also indicate that the major uncertainty factor is the variation of water content. To minimize it, classification of rough water fill ratio in a canister such as wet storage or dry storage will be required.